Wide Binaries
Self-Eliminating — Pending External Adjudication (2026)Wide binary star systems — two stars orbiting each other at separations of thousands of AU — provide one of the cleanest tests of gravity in the low-acceleration regime. Synchronism makes a specific, testable prediction about these systems that differs from both Newtonian gravity and standard MOND.
Why Wide Binaries?
At separations greater than ~104 AU (roughly 0.05 parsecs), the gravitational acceleration between two stars drops below a₀ ≈ 1.2 × 10−10m/s². In Newtonian gravity, nothing special happens. In MOND, orbital velocities should be higher than Newtonian predictions. The anomaly — if it exists — should be visible in the orbital dynamics.
The beauty of wide binaries is simplicity: two gravitating masses, no dark matter halo ambiguity, no complex baryonic physics. It is the closest thing to a clean two-body test of modified gravity.
Synchronism's Prediction
Standard MOND predicts the same anomaly regardless of where the binary system is located. Synchronism predicts something different:
Density-Dependent Anomaly
The wide binary anomaly should depend on local environment density. Binaries in dense stellar neighborhoods (near the Galactic plane, in open clusters) should show a weaker anomaly than binaries in low-density environments (high Galactic latitude, far from molecular clouds).
This follows directly from the coherence function: higher ambient density shifts ρcrit, altering the acceleration threshold at which modified dynamics appear. In dense environments, the external coherence field “masks” the low-acceleration effects.
Predicted amplitude: In the clean within-250-pc Gaia sample, C(ρ) predicts only 0.05–0.4% velocity deviation from Newtonian dynamics — because the C(ρ) prediction for wide binaries is effectively the Newtonian null (g_eff ≈ g_N at the relevant densities). This is ~80× below Gaia DR3 wide-binary systematics. Cf. MOND prediction: ~18% velocity enhancement. The amplitude difference is fundamental, not instrumental.
The Data
The European Space Agency's Gaia mission (Data Release 3) provides the necessary measurements: positions, proper motions, parallaxes, and radial velocities for over a billion stars. From this, wide binary candidates can be identified and their orbital dynamics characterized. Gaia Archive (ESA) →
Feasibility Kill — Signal Below Gaia Systematics
Current Observational Status (updated 2026-06-23)
The wide-binary debate escalated in 2026. The earlier dispute (sample selection, contamination, statistical cuts) has been superseded by a sharper disagreement:
- Chae et al. 2026 (arXiv:2601.21728): Enlarged RV+speckle-vetted sample of 36 binaries → 4.9σ boost with γ_boost ≈ 1.6 — consistent with MOND.
- Saad & Ting 2026 (arXiv:2603.11015): Reanalyzed the same 36 binaries from Chae et al. 2026 using a hierarchical semi-major-axis fit (replacing geometric deprojection) → γ = 1.12 ± 0.25, Newton-consistent at 0.4σ. The entire anomaly lives in one modeling assumption (orbital deprojection prior).
- Prior generation (2023–2024): Banik et al. (2024), Pittordis & Sutherland (2023), Saurabh & Desmond (2024) all Newtonian-consistent with different cuts.
- Hernandez (2023–2024): Anomalies in projected-velocity statistics; methodology disputed.
Why This Test Cannot Be Decisive (As Currently Formulated)
If anomaly confirmed (Chae wins)
C(ρ) predicts the Newtonian null — so a confirmed MOND-scale anomaly would refute C(ρ) (it predicts ~0.05–0.4%, not ~18%). The “kill branch” fires with existing data if Chae's deprojection approach is vindicated.
If null confirmed (Banik wins)
C(ρ) survives — but degenerately with Newton. The predicted signal (0.05–0.4%) sits 80× below Gaia DR3 systematics, so there is no measurement that selects Synchronism over Newton.